Downloaded directly from Apple
https://support.apple.com/en-us/HT211683
or
https://web.archive.org/web/20210802172226/https://support.apple.com/en-us/HT211683
It's NOT an iso file and will not work in vmware or virtual box.
This is a .dmg file that can be read ONLY by PCs that run mac os already. Windows can't read HFS+ file system, if you want to read the file on a windows computer you will need a program like HFS Explorer or MacDrive 10
You can use it to make an installation USB drive